Device for indicating underinflation of tires



May 25, 1948. H [l TWOMBLY 2,442,104

DEVICE FOR INDICATINQl UNDER INFLA'TION OF TIRES Filed July 30, 1945 INVENTOR ATTORNEYv Patented May 1948 UNITED STATES PATENT OFFICE t DEVICE FORINDCATING UNDERINFLATION OF TIRES Application July 30, 1945, Serial No. 607,853

l 2 Claims.

This invention relates generally to pneumatic tires and particularly to a means for indicating the under-inflation thereof.4

The main object of this invention is to provide a means for automatically indicating when a tire is under-inilated, or overheated.

The second object is to provide a device of the class described in which the indication is made by heat responsive means which is exceedingly rugged in construction and yet responsive to small changes in temperature.

I accomplish these and other objects in the manner set forth in the following specification, as illustrated in ythe accompanying drawing in which:

Fig. 1 is a diagrammatic view showing the general arrangement of the device and showing the thermostatic element broken away in section.

Fig. 2 is a transverse section through a tire intersecting the thermostatic element along the line 2-2 in Fig. 1.

Fig. 3 is a fragmentary section taken along the A line 3--3 in Fig. 1.

Similar numerals refer to similar parts throughout the several views.

Referring in detail to the drawing there is showna common form of outer casing I within which is mounted the usual irmer tube II, both of which are mounted on the wheel I2. The usual form of air valve Il is employed, but for the purpose of this invention it is illustrated as passing through the thermostatic element for positioning same.

Referring to the thermostat, same will be seen to consist of a curved hollow casing I4 preferably of a heat absorbing metal such as aluminum and having theinner curve I5 corresponding with the interior surfacejl of the inner tube Il. The top side I1 of the casing I4 is preferably flat although it may assume any other desired shape.

Within the casing I4 is mounted a double leaf bi-metallic element consisting of the parts IB and I. which differ yfrom those commonly employed in that portions having equal co-efllcients of expansion are in contact with each other and those portions having other co-eillcients of expansion are not touching each other, the members I8 and I8 being held together by means of the rivets 20.

The member I8 bears against the adjusting screw 2| mounted in the side of the casing Il while the member I9 is secured to the terminal 22 which is mounted in the casing Il, and insulated therefrom by means cf a bushing 23. The

end 24- of the members I8 and I9 is free to float within the casing I4.

The terminal 22 is connected by means of a lead 2l with a brush 28 which rides upon a contact ring 21 which may consist of the brake drum itself or a special ring mounted thereon, or on some part of the wheel upon which the tire can be mounted.

A second brush 28 rides on the ring 21 and its lead 29 is connected to the lamp Il, preferably on the instrument panel in the cab. Current is supplied to the lamp 30 from the battery 3| which is connected by means of the lead 32 to the casing I4.

While various means may lbe employed to accomplish this purpose, it is necessary to employ a heat responsive element which can be accurately adjusted before its insertion into the casing. In

some forms of the device the thermostatic element is mounted between the inner tube II and the casing I0 which facilitates the insertion and removal thereof although it is somewhat less sensitive in its responsive action.

The operation or the device is as follows: Assuming that the tire III is in operation and that its pressure falls below a predetermined minimum causing thewalls of the casingI I0 to flex objectionably thereby building up a heat within the tire I0, the developed heat is absorbed in part by the casing I4 and through the action of the elements I8 and I! the circuit is closed through the member indicating to the driver 30 that one of his tires is under-inflated.

0f course it is immaterial which tire is underinflated and when the tires are inspected he can readily determine which tire is under-innated. It will be understood, of course, that each wheel is equipped with the thermostatic device and all of the leads may control the single lamp or they may be grouped for wheels, or axles or vehicles depending on the nature of installation. In some cases, it will be found desirable to employ a thermo-couple instead of a thermostat in order to indicate the temperature differences, in which case the elements might Ibe varied but the principle employed and results obtained, remain the same. Namely, that an indication is given of a temperature increase within a tire due either to the flexing of an under-inflated tire or the overinilating of a tire, due to its companion tire being under-inflated. While the leads 25 and l2 are shown directly connected to the brushes 2l and 26 in Fig. 1, it is obvious that the circuit must pass through the inner tube Il. This is accomplished by connecting the lead 32 to the tire Naive stem Il and passing the lead 2l through the tube II as shown in Fig. 2. u While I have thus illustrated and described 2. In a pneumatic wheel the combination oi' it= ll 1,895,295

rim having a pneumatic tire mounted on the outer side thereof, the inner side of said tire engaging said rim, being disposed around the median plane of said tire. a heat responsive switch disposed within said tire along said space and attached to the air inlet valve, and an electrically operated indicator controlled by said heat responsive 5 means for indicating an over-temperature within said tire.

HARRY D. TWOMBLY.

REFERENCES CITED The following references are of record in the ille ofv this patent:

UNITED STATES PATENTS Number Name Date Rollins Dec. 18, 1928 '1,907,540 Hebler May 9, 1933 1,945,017 Beach Jan. 30, 1934 2,159,342 Persons May 23, 1939 

